This invention relates to a method and apparatus for projecting spatially correct seismic data onto a large three-dimensional (3D) curved display surface, to aid in interpretation of geological characteristics of the earth. More specifically, this invention relates to a method for projecting computer graphic video images of seismic data onto a large curved 3D display surface, allowing viewers to interact with the 3D display, and to use their peripheral vision, and thus perceive the displayed imagery with a sense of realism comparable with natural viewing of a 3D physical reality.
For many years seismic exploration for oil and gas has involved the use of a source of seismic energy and its reception by an array of seismic detectors, generally referred to as geophones. When used on land, the source of seismic energy can be a high explosive charge electrically detonated in a borehole located at a selected point on the terrain, or another energy source having capacity for delivering a series of impacts or mechanical vibrations to the earth""s surface. Offshore, air gun sources and hydrophone receivers are commonly used. The acoustic waves generated in the earth by these sources are reflected back from strata boundary and/or other discontinuities and reach the earth""s surface at varying intervals of time, depending on the distance traversed and the characteristics of the subsurface traversed. On land these returning waves are detected by the geophones, which function to transduce such acoustic waves into representative electrical analog signals, which are generally referred to as traces. In use on land an array of geophones is generally laid out along a grid covering an area of interest to form a group of spaced apart observation stations within a desired locality to enable construction of three-dimensional views of reflector positions over wide areas. The source, which is offset a desired distance from the geophones, injects acoustic signals into the earth, and the detected signals at each geophone in the array are recorded for later processing using digital computers, where the analog data is generally quantized as digital sample points, e.g., one sample every two milliseconds, such that each sample point may be operated on individually. The geophone array is then moved to a new position and the process is repeated to obtain a 3D data volume for a seismic survey.
After exploration of an area is completed, data relating to energy detected at a plurality of geophones will have been recorded, where the geophones are located at varying distances from the shotpoint. The data is then reorganized to collect traces from data transmitted at various shotpoints and recorded at various geophone locations, where the traces are grouped such that the reflections can be assumed to have been reflected from a particular point within the earth, i.e., a common midpoint. The individual records or xe2x80x9ctracesxe2x80x9d are then corrected for the differing distance the seismic energy travels through the earth from the corresponding shotpoints, to the common midpoint, and upwardly to the various geophones. This step includes correction for the varying velocities through rock layers of different types and changes in the source and receiver depths. The correction for the varying spacing of shotpoint/geophone pairs is referred to as xe2x80x9cnormal move out.xe2x80x9d After this is done, the group of signals from the various midpoints are summed. Because the seismic signals are of a sinusoidal nature, the summation process serves to reduce noise in the seismic record, and thus increasing its signal-to-noise ratio. This process is referred to as the xe2x80x9cstackingxe2x80x9d of common midpoint data, and is well known to those skilled in the art. Accordingly, seismic field data undergoes the above-mentioned corrections, and may also undergo migration, which is an operation on uninterpreted data and involves rearranging of seismic information so that dipping horizons are plotted in their true location. Other more exotic known processing techniques may also be applied, which for example enhance faults and stratigraphic features or some other attribute, before the continuously recorded traces are reduced to vertical or horizontal cross sections or horizontal map views which approximate subsurface structure, and are usually in color.
Once the seismic data is satisfactorily processed to incorporate necessary corrections and desired enhancements, the geophysicist interprets the 3D seismic information. In general terms, interpretation involves deriving a simple plausible geological subterranean model that is compatible with the observed data. This model is never unique, and discovering it involves a sequence of somewhat arbitrary choices.
Despite significant progress in interactive 3D seismic interpretation systems, seismic workstations continue to rely on vertically and horizontally displayed planar slices of recorded data to provide almost all of the xe2x80x9cworking surfacesxe2x80x9d for horizon and fault picking, and correlation. These planar slices provide only a limited perspective of the full three dimensional picture. Often animation of successive slices is required to provide information about the third dimension. However, animation intrinsically forces a three-dimensional interpretation based on the interpreter""s memory of the changing picture through time, rather than on direct comparison and correlation of the data.
In observing and interpreting the seismic information displaying in a useful form is highly advantageous. Display systems are widely used in diverse image display applications, with most systems employing either planar or substantially planar display surfaces, i.e., flat wall screens which have an inherently limited field of view. While it is possible to extend the observers field of view by simply increasing the vertical and horizontal dimensions of the planar display screen, this expansion generally results in an unacceptable level of distortion of the image. In order to permit users to view objects peripherally, display technology has been developed which generally uses multiple projectors to project adjoining images on adjacent sections of a large wraparound screen so that observers can view objects with depth perception in 3D space.
Accordingly, four screen types are commonly used today to facilitate the many diverse image display applications. These four screen types are: 1) a flat wall, 2) multiple adjacent flat walls, 3) a dome, and 4) a curved wraparound panel, which can be semi-toroidal. All of these display surfaces can include stereo 3D graphics, and some applications require it to be successful.
The reason that no one screen type has persisted is that the different problems and purposes encountered with display systems are best individually addressed by only one of the various screen types mentioned above.
Accordingly, it is an object of this invention to provide a hybrid screen that combines the four screen types in a unitary structure.
A more specific object is to provide a hybrid screen for viewing various 3D combinations of wraparound, dome, flat wall and multi-wall type displays using a single video projector or multiple video projectors.
A still more specific object of this invention is to provide a portable, self-supporting rigid structure with a concave inner viewing surface, which is suitable for positioning on a desktop or on a moveable support table.
Yet another object is to provide an economical viewing surface that gives the viewer a sense of depth perception without requiring stereo projection and stereo glasses.
It is still another object of this invention to create a truly three-dimensional interactive graphic workstation to aid in geological interpretation of seismic data.
A more specific object of this invention is to visualize spatially correct seismic data on a large concave screen that facilitates horizon and fault mapping of seismic data.
Still another object is to provide a projection system for computer graphic images of seismic data that includes a portable self-supporting rigid screen with a concave inner display surface, which is economical in cost, and includes about fifty times more viewing area compared to conventional seismic workstation monitors.
Another more specific object of this invention is to provide a desk-top-based projection system having a concave screen, and a projector located about nine feet in front of the curved screen for use in interactive desk top viewing environments.
A further object is to provide a projection display system which can be used to view large scale monoscopic as well as stereoscopic color imagery of three-dimensional seismic data.
While the invention below is described in terms of mapping and projected 3D seismic data, it should be understood that the techniques described herein can be adapted to mapping and projecting 3D data in other fields, such as medical displays, video games and scientific 3D viewing. Accordingly, the invention claimed below should not be construed as limited for use with 3D seismic data.
According to the present invention the foregoing and other objects and advantages are attained in a method and apparatus for extracting, mapping and projecting 3D seismic data to its spatially correct location on a relatively large concave 3D display surface. The method is based on computer software, and involves storing a volume of digitally formatted seismic data in memory of a suitable computer as a first step. A mathematical model is then created corresponding to the shape of the concave 3D display surface, and the mathematical model is inserted in the computer memory so as to at least partially intersect the seismic data volume. The intersecting seismic data is extracted and mapped onto an image plane. Next, the extracted data is processed using digital computational techniques so as to maintain correct spatial position for the varying projector to screen distances associated with the concave 3D display surface, and is then projected onto the concave display surface in its spatially correct dimensions. This means that the displayed seismic data is not a vertical slice of seismic data projected onto a curved screen, but is data carved out of the 3D data volume corresponding to the shape of the concave display surface.
Accordingly, the apparatus of this invention includes a relatively large 3D display surface compared to a typical CRT monitor screen, and which is suitable for positioning on a desk or tabletop. The presently preferred display surface is a multi-section hybrid projection screen structure having a concave display surface for viewing video images. This presently preferred 3D display surface facilitates viewing on four commonly used screen types including: a flat wall, multiple adjacent flat walls, a concave semidome, and a semicylindrical wraparound screen. The various screen types are combined into a single screen referred to herein as a xe2x80x9chybridxe2x80x9d screen, which includes three sections, i.e., a ceiling section which is a concave semidome extending 180 degrees horizontally, and 90 degrees vertically, a semicylindrical lower screen panel, and a flat semicircular floor section. The semidome is elevated above the desktop supported by the cylindrical lower section which is edgewise connected to the semidome. The semicircular floor area completes the display surface. A video projector for displaying the seismic data, which allows the high speed graphic output of a computer system to be projected, enlarged and focused onto a concave screen, is located at a convenient distance from the display surface. Accordingly, computer generated signals control the view to be displayed, and the views include animation of successive images derived from the volume of data to display spatially correct seismic information throughout the data volume.
Also connected to the computer, or parallel computers as the case may be, can be a keyboard, a mouse, two CRT seismic workstation monitors and a relatively small flat auxiliary screen in the shape of a paddle, that can be held by the geophysicist and positioned within the volume inside of the larger concave display.
In a preferred embodiment, the 3D display surface is a unitary construction that combines viewing features of the four commonly used screen types including: a flat wall, multiple adjacent walls, a semidome, and a wraparound. Accordingly, the display surface includes multiple sections for viewing 3D displays. Various combinations of these sections may also be used for viewing, such as the semidome ceiling section together with the flat wall, and, further, the various sections can be divided into subsections or subareas for detailed viewing.
In use, a video projector, which accepts multiple simultaneous inputs, is connected to a computer to allow the graphic output of the computer to be projected, enlarged, and focused onto the hybrid screen. Accordingly, computer generated signals control the view to be displayed, and the views include section or subsection displays, as well as animation of successive views, which imparts lifelike motion to an object and which is derived from the volume of data, to display information from throughout the data volume.
In another preferred embodiment, a relatively small flat auxiliary screen in the shape of a paddle is provided. This paddle screen can be held by the viewer and positioned within the volume inside of the hybrid screen. An electromagnetic transmitter mounted on the outside of the concave screen surface in combination with a receiver mounted on the paddle screen detect the position and orientation of the moveable paddle throughout the space defined within the hybrid screen, and an interactive image is displayed on the paddle, representing the data that exists at the detected spatial position. Thus, the paddle can be used for exploring the volume within the hybrid screen. In simulation displays, the image on the paddle could represent a view corresponding to a rear view mirror. Further, in mining or seismic displays, the paddle can display petrophysical properties of rocks or acoustic waves that are present at that relative position in the interior of the concave display surface.
The method and apparatus of this invention using a large 3D display surface, thus can display a variety of useful views, which are helpful in picking or interpreting seismic horizons and fault segments observed on the surface of the hybrid screen. These views include: 1) a wraparound 180-degree display using only the semicylindrical lower portion of the screen, 2) a 180-degree by 90-degree dome display using the semidome ceiling only, 3) a 1 80-degree wraparound plus floor display using the combination of the semicylindrical lower screen panel and the floor, 4) a single wall or a three-wall display using the semicylindrical lower screen panel divided into three subareas, 5) a single wall plus floor using the combination of a subarea of the semicylindrical lower screen panel and the floor, and 6) a silo with a floor, where the entire concave display surface is illuminated. In addition, the software incorporates real-time navigation through a data volume, and facilitates interactive features including: translate, zoom and rotate. This provides the user with full flexibility to explore the entire data volume, and simplifies quick interactive reconnaissance viewing of the 3D seismic data volume from a variety of viewpoints.
Still other objects and advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description and the drawings, wherein there is shown and described only one of the several preferred embodiments of the invention. While the best mode contemplated for carrying out the invention is illustrated as applied to a particularly shaped concave 3D display surface, it will be realized that the invention is suitable for other and different embodiments such as projecting the spatially correct seismic surfaces, or any other data formatted as a 3D digital volume, onto any desired shaped surface, such as the interior of a hemispherical display surface, the outer surface of a sphere, a corner between walls or a flexible screen curved to a desired shape. Also several details of the invention are subject to modification in various obvious respects, all without departing from the invention. Accordingly, the description of the invention and the drawings are to be regarded as illustrative in nature, and not as restrictive.